Although the appearance of the conventional sail is quite different from that of an aircraft wing, its function in generating a positive force is based on the same aerodynamic principles as the wing. Parenthetically, it should be noted that in referring to positive force when comparing a wing to a sail, one is referring to "lift" in a wing and "thrust" in a sail. The sail, however, is considerably the less productive of the two. This is partly because the sail utilizes a single surface air foil as opposed to the more efficient double surface air foil of the wing.
Another factor that reduces the efficiency of a conventional sail is its external bracing, mast and rigging, which disturbs the flow of air around its surface, resulting in an energy loss to turbulence and drag.
Inspite of its much greater efficiency, a standard wing does not make a good sail when mounted in a vertical position so that the lift that it generates can be used as thrust to drive a boat or vehicle. This is because of the shape of the wing and the fact that in use wind is directed against both sides of the wing at various angles. In this regard, it should be appreciated as the wind approaches a conventional wing at a positive angle of attack from what was its bottom surface, the wing will produce good results and significantly improve the efficiency over the conventional sail. But when the wind is directed from a direction where the same impinges on the upper surface of a conventional wing, its efficiency drops well below that of the sail.
Consequently, it follows that in order to provide an all around efficient wing for "sailing purposes" that it would be desirable to design the same to have a changeable air foil, or variable camber. This would enable the wing to have the high efficiency referred to with the wind approaching the same from either side.
It should be noted that the provision of a variable camber wing for a vessel has been provided in the past. A close review of the prior art in this area reveals that the design and construction of such variable camber wings have been complex and in fact impractical when considered on a commercial production basis.
Because of the increases in efficiency achieved by such a variable camber wing, it is highly desirable that a relatively simple and easy to use design be provided that lends itself to commercial production.